1. Field of the Invention
The present invention generally relates to Power over Ethernet (PoE) devices, and more specifically to efficient communications between a PoE subsystem, power source equipment (PSE) subsystems, and switching subsystems.
2. Related Art
Ethernet communications provide high speed data communications over a communications link between two communications nodes that operate according the IEEE 802 Ethernet Standard. The communications medium between the two nodes can be twisted pair wires for Ethernet, or other types communications medium that are appropriate. PoE communication systems provide power and data communications over a common communications link. More specifically, a PSE device connected to the physical layer of the first node of the communications link provides direct current (DC) power (for example, 48 volts DC) to a powered device (PD) at the second node of the communications link. The DC power is transmitted simultaneously over the same communications medium with the high speed data from one node to the other node.
Example PD devices that utilize PoE include Internet Protocol (IP) phones, wireless access points, etc. The PSE subsystem is often a data switch having at least two rows of data ports, where a data port in the input row of data ports can be switched to any one of the data ports in the output row of data ports. Each data port typically includes a serial-to-parallel (i.e. SERDES) transceiver, and/or a PHY device, to support high speed serial data transport. Herein, data ports and their corresponding links can be interchangeably referred to as data channels, communication links, data links, etc, for ease of discussion.
On the PSE chip portion of the PoE device, the DC voltage supply circuit provides a voltage, e.g., 48 volts, to power the PD. The DC voltage supply and its corresponding output voltage, are controlled by the PSE controller. For example, the PSE controller includes a switch connected across output terminals of the DC voltage supply circuit for determining when its output voltage is switched on or off. The PSE subsystem also performs functions such as discovering a presence of PD devices by checking for characteristic resistances, managing/integrating power, and monitoring current draw.
Within a PoE communications system, two power domains are present having two separate ground references. An isolation transformer is provided to isolate one ground reference system (i.e., the wire side of the system) from the other ground reference system (i.e., the system side). Accordingly, an isolation boundary is provided such that when an energy pulse is injected on the wire (e.g., Ethernet cable) relative to the ground of the connector, that ground is electrically isolated from the ground reference system for the remaining electronics behind the transformer.
The PoE device fundamentally sits on the wire side of the transformer so it is under the other ground system. Because of the isolation and floating ground references, if the PoE communications system needs to communicate or be controlled by an electronic subsystem on the other side of the transformers (non-wire or isolated side), then the isolation boundary must be crossed.
One of the most common ways of crossing the isolation boundary is to use opto-isolators or opto-coupling devices. Opto-isolators can be placed along the feedback path between the PSE controller and the PHY. As understood by those of skill in the art, opto-isolators are made up of a light emitting device, and a light sensitive device, wrapped in a single package, but having no electrical connection between the two. A beam of light facilitates transmission of the signals across the isolation boundary. The light emitter is nearly always an LED.
An important aspect of conventional PoE communications system is the ability to connect the PoE device to a host subsystem within the PoE communications system. This connection provides configuration, control, and status reporting between the PoE subsystem, the PHY subsystem, and the switching subsystem. The conventional PoE communications systems, however, waste multiple communication paths between host and PoE as well as host and PHY/switch. That is, these additional communications paths require additional control interfaces and additional control circuitry/modules etc.
Furthermore, in these conventional communications systems, the PoE interface is unique, and is specific to a control logic/module that interacts with the host subsystems. The unique nature of this interface complicates the ability to mix and match switch and PHY technologies with PoE technologies without knowing of, or having control circuitry that is specific to each solution.
What is needed, therefore, is a more efficient and flexible way to connect PoE technologies to the host that would reduce the number of interfaces and control/logic modules and allow for an easy mix and match of switch and PHY solutions with PoE solutions. What is also needed is an ability to mix and match switch and PHY technologies without concern for the type of control interface present on the PoE and without knowledge of what control modules are needed for the switching subsystem and/or the PHY subsystem.